Because an earlier filing date allows patenting of inventions that might otherwise have been "anticipated" by one or more "references" (i.e., made unpatentable due to the existence of "prior art"), it is advantageous to take advantage of prior filings of the first patent application disclosing an invention (called the "parent" application), even if the patent office in which it was filed is in a foreign country. Provided the foreign country affords similar rights, this is done by filing in the U.S. a patent application "claiming" priority of invention in the foreign country within twelve months of having filed the foreign or international patent application.
Law - Priority Claims(s)